Passing Sight Distance Tool
One of the most tedious steps in finishing a road design has been establishing the passing and no passing zones for the permanent traffic control plan. Many attempts have been made to develop a means by which to determine the passing and no-passing zones. The most common is outlined in the AASHTO 2001 Green Book, pages 127 - 131, (sometimes referred to as The Rolling Straight Edge method). I've even heard of two guys, in different vehicles, with 2-way radios, trying to maintain the minimum passing distance between themselves and when they got out of sight of each other, they each threw a handful of flour out the window . . . a wild approach, especially on a windy day in Wyoming! The Federal Highway Administration had an application written for RDS that was quite good. When RDS was replaced with GEOPAK, we no longer had the ability to easily determine the passing/no passing areas.
Once brought to GEOPAK's attention, they developed this tool. It's all based on creating a 3D model of your proposed design.
To use this application, the following files are necessary:
- The GPK file with the stored alignments.
- A TIN file that reflects your proposed design.
- Any 2D or 3D design file. This file can be totally blank, but if a 3D design file is used and a proposed 3D model is created, you will be able to see the "sight" lines being drawn.
STEP 1: Create a TIN File
The easiest way to do this is to open your proposed cross section file and invoke the XS Report dialog...
NOTE: This routine does not recognize vertical slopes in the cross section file, (a DTM problem). Modify any vertical slopes so that they're not exactly vertical.
Invoke the XS Report dialog:
APPLICATIONS > GEOPAK ROAD > CROSS SECTIONS > REPORTS and Select... DTM Prop 3D.
This invokes the DTM Proposed 3D Report dialog, and the sole purpose of this step is to create a .DAT file that will eventually create the .TIN file representing your proposed design.
Key in all appropriate information in the fields.
NOTE: The default extension for the output file will be .COL, remember to change this to .DAT.
Click on Apply.
STEP 2: Create the TIN File
Open any 2D or 3D design file and invoke the DTM dialog...
APPLICATIONS > GEOPAK ROAD > DTM TOOLS and select the icon... DTM Menu. Next select Build > Triangles
Use the Files picker to select the .DAT file that you created.
Enter the path and name of the .TIN file to create.
Toggle Dissolve Option to Side.
Key in the Side Length. (200 for English, 60 for Metric seems to work most of the time).
Click on Process. Proceed to Final Step if Step 2 is skipped.
FINAL STEP
To invoke the Passing Sight Distance dialog box:
APPLICATIONS > GEOPAK ROAD > 3D TOOLS > Passing Sight Distance
- Select the Tin file using the Browse icon. This is the TIN file that was created in Step 1 and/or Step 2 of these instructions.
- Select the Job Number from the drop down arrow.
- Select the Chain using the Browse icon.
- The beginning and ending stations can be entered manually or by using the DP buttons and snapping to a graphical element in the design file.
- A normal sampling increment for an English design would be 50 ft. This simply tells the program what frequency to check for sight distance. Metric, maybe use 15 m.
Under Design Parameters:
Click on Driver / Visible Vehicle Location:
Driver Location:
- Height Above TIN . . . AASHTO recommends using an average driver's eye height of 3.5 ft., (1.07 m).
- Direction of Stationing Offset . . . For a typical two lane highway, the driver would normally be approximately 4 ft., (1.22 m) from centerline.
- Opposite Direction of Sta. Offset . . . Again, for a typical two lane highway, the driver would normally be approximately 4 ft., (1.22 m) from centerline.
Visible Vehicle Location:
- Height Above TIN . . . AASHTO recommends using an average driver's eye height of 3.5 ft., (1.07 m).
- Direction of Stationing Offset . . . For a typical two lane highway, the driver would normally be approximately 4 ft., (1.22 m) from centerline.
- Opposite Direction of Sta. Offset . . . Again, for a typical two lane highway, the driver would normally be approximately 4 ft., (1.22 m) from centerline.
Still under Design Parameters:
Additional No Passing Distance . . . This is more or less a safety buffer that adds whatever distance is keyed in to each end of a no-passing zone. For instance if the program determines that your design has a no-passing zone from 12+50 to 15+00 and you've keyed 25 in this field . . . a no-passing zone will be calculated from 12+25 to 15+25. If no additional distance is desired, key in 1, zero is invalid.
Minimum Passing Zone Length . . . AASHTO refers the marking of no-passing zones to the MUTCD manual. The MUTCD manual states, "Where the distance between successive no-passing zones is less than 400 feet, the appropriate no-passing marking (one direction or two direction) should connect the zones." FHWA will be using the 400-foot (122 m) distance as a minimum passing zone length.
Zone Designation:
When pressed this button invokes the Zone Designation Table. This optional dialog is intended for designating certain areas to be treated specially. In addition to specifying station ranges, there are two other options for more specific consideration:
Side . . . three options, Left, Right and Both
Class . . . three options, Passing, No-Passing, and Void.
For example, if the design was going through an area that was to be double yellow striped due to it being a heavy congested area, the user would key in the Beginning and Ending Station, toggle the Side toggle to Both, toggle the Class toggle to No-Passing and click on Add. A series of station ranges and Side/Class options can be saved via the File pulldown and loaded again later for additional processing.
Sight Distance:
When pressed this button invokes the Sight Distance Table. This is where the various design speeds are identified. Rather than input the design speed the Minimum passing sight distance is entered. This table allows the user to have multiple design speeds within the design and have each calculated according to its station range. These ranges and passing sight distances can be saved via the File pulldown and loaded again later for additional processing.
Under Output Options:
The Draw Striping and Stripe Pattern button actually draw the pavement markings in a 2D design file. When the Stripe Pattern button is pressed, the user keys in the appropriate data for stripe length/skip and offsets. When either the Solid or the Skip button is pressed, the Design and Computation Manager is invoked and allows the user to select the appropriate pay item to be drawn in the 2D DGN file.
The Create Report toggle and its Browse icon, are used for identifying the name of the output file and its path. This is the ASCII output file that actually displays the passing and no-passing zones.
The Draw Sight Lines option allows the user to actually draw "sight lines" based on the Sampling Increment and Sight Distance values. These lines can be drawn Temporarily or Permanently.
The Sight Line Symbology settings buttons (for left and right) are where the user decides the levels, colors, weights and line styles that the sight lines are to be drawn. To adjust these settings, double click in the Left and Right rectangle areas of the dialog.
When finished with all the dialog boxes and tables, press Apply at the bottom of the Passing Sight Distance dialog box.
Most likely, you will encounter the following 2 "Information" dialogs:
Remember, the application is based on a proposed TIN file. The application doesn't know anything about what exists outside of the proposed TIN file. These Information boxes are simply saying that it can't look outside of the TIN to determine whether it's safe to pass or not.
As a result, you must determine the passing/no passing zones at the beginning and ends of your project manually. These manually determined values are then entered into the Zone Designation dialog.
The undetermined areas can be viewed in the Report.
Once the Zone Designation dialog is competed, click on Apply once again.
As mentioned earlier, the results can be reviewed in the ASCII .txt file. A sample is illustrated below:
Solid Left Skip Center Solid Right
---------- ----------- -----------
10+001.00 R 1 to 11+200.00 R 1 11+125.78 R 1 to 11+717.97 R 1 10+000.00 R 1 to 11+125.78 R 1
11+655.47 R 1 to 13+220.79 R 1 12+328.91 R 1 to 12+730.47 R 1 11+717.97 R 1 to 12+328.91 R 1
12+827.34 R 1 to 13+220.79 R 1 12+730.47 R 1 to 12+827.34 R 1
Total: 2764.32 1387.20 1833.59